/**
 * Copyright (c) 2012-2016, www.tinygroup.org (luo_guo@icloud.com).
 * <p>
 * Licensed under the GPL, Version 3.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * <p>
 * http://www.gnu.org/licenses/gpl.html
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.tinygroup.commons.namediscover;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.objectweb.asm.*;
import org.tinygroup.commons.asm.EmptyVisitor;
import org.tinygroup.commons.tools.ClassUtils;

import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Constructor;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.util.Collections;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 *
 * @author renhui
 *
 */
public class LocalVariableTableParameterNameDiscoverer implements ParameterNameDiscoverer {

    // marker object for classes that do not have any debug info
    private static final Map<Member, String[]> NO_DEBUG_INFO_MAP = Collections.emptyMap();
    private static Log logger = LogFactory.getLog(LocalVariableTableParameterNameDiscoverer.class);
    // the cache uses a nested index (value is a map) to keep the top level cache relatively small in size
    private final Map<Class<?>, Map<Member, String[]>> parameterNamesCache =
            new ConcurrentHashMap<Class<?>, Map<Member, String[]>>();


    public String[] getParameterNames(Method method) {
        Class<?> declaringClass = method.getDeclaringClass();
        Map<Member, String[]> map = this.parameterNamesCache.get(declaringClass);
        if (map == null) {
            // initialize cache
            map = inspectClass(declaringClass);
            this.parameterNamesCache.put(declaringClass, map);
        }
        if (map != NO_DEBUG_INFO_MAP) {
            return map.get(method);
        }
        return null;
    }

    public String[] getParameterNames(Constructor ctor) {
        Class<?> declaringClass = ctor.getDeclaringClass();
        Map<Member, String[]> map = this.parameterNamesCache.get(declaringClass);
        if (map == null) {
            // initialize cache
            map = inspectClass(declaringClass);
            this.parameterNamesCache.put(declaringClass, map);
        }
        if (map != NO_DEBUG_INFO_MAP) {
            return map.get(ctor);
        }

        return null;
    }

    /**
     * Inspects the target class. Exceptions will be logged and a maker map returned
     * to indicate the lack of debug information.
     */
    private Map<Member, String[]> inspectClass(Class<?> clazz) {
        InputStream is = clazz.getResourceAsStream(ClassUtils.getClassFileName(clazz));
        if (is == null) {
            // We couldn't load the class file, which is not fatal as it
            // simply means this method of discovering parameter names won't work.
            if (logger.isDebugEnabled()) {
                logger.debug("Cannot find '.class' file for class [" + clazz
                        + "] - unable to determine constructors/methods parameter names");
            }
            return NO_DEBUG_INFO_MAP;
        }
        try {
            ClassReader classReader = new ClassReader(is);
            Map<Member, String[]> map = new ConcurrentHashMap<Member, String[]>();
            classReader.accept(new ParameterNameDiscoveringVisitor(clazz, map), ClassReader.EXPAND_FRAMES);
            return map;
        } catch (IOException ex) {
            if (logger.isDebugEnabled()) {
                logger.debug("Exception thrown while reading '.class' file for class [" + clazz
                        + "] - unable to determine constructors/methods parameter names", ex);
            }
        } finally {
            try {
                is.close();
            } catch (IOException ex) {
                // ignore
            }
        }
        return NO_DEBUG_INFO_MAP;
    }


    /**
     * Helper class that inspects all methods (constructor included) and then
     * attempts to find the parameter names for that member.
     */
    private static class ParameterNameDiscoveringVisitor extends EmptyVisitor {

        private static final String STATIC_CLASS_INIT = "<clinit>";

        private final Class<?> clazz;
        private final Map<Member, String[]> memberMap;

        public ParameterNameDiscoveringVisitor(Class<?> clazz, Map<Member, String[]> memberMap) {
            this.clazz = clazz;
            this.memberMap = memberMap;
        }

        private static boolean isSyntheticOrBridged(int access) {
            return (((access & Opcodes.ACC_SYNTHETIC) | (access & Opcodes.ACC_BRIDGE)) > 0);
        }

        private static boolean isStatic(int access) {
            return ((access & Opcodes.ACC_STATIC) > 0);
        }

        @Override
        public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
            // exclude synthetic + bridged && static class initialization
            if (!isSyntheticOrBridged(access) && !STATIC_CLASS_INIT.equals(name)) {
                return new LocalVariableTableVisitor(clazz, memberMap, name, desc, isStatic(access));
            }
            return null;
        }
    }


    private static class LocalVariableTableVisitor extends EmptyVisitor {

        private static final String CONSTRUCTOR = "<init>";

        private final Class<?> clazz;
        private final Map<Member, String[]> memberMap;
        private final String name;
        private final Type[] args;
        private final boolean isStatic;
        /*
         * The nth entry contains the slot index of the LVT table entry holding the
         * argument name for the nth parameter.
         */
        private final int[] lvtSlotIndex;
        private String[] parameterNames;
        private boolean hasLvtInfo = false;

        public LocalVariableTableVisitor(Class<?> clazz, Map<Member, String[]> map, String name, String desc,
                                         boolean isStatic) {
            this.clazz = clazz;
            this.memberMap = map;
            this.name = name;
            // determine args
            args = Type.getArgumentTypes(desc);
            this.parameterNames = new String[args.length];
            this.isStatic = isStatic;
            this.lvtSlotIndex = computeLvtSlotIndices(isStatic, args);
        }

        private static int[] computeLvtSlotIndices(boolean isStatic, Type[] paramTypes) {
            int[] lvtIndex = new int[paramTypes.length];
            int nextIndex = (isStatic ? 0 : 1);
            for (int i = 0; i < paramTypes.length; i++) {
                lvtIndex[i] = nextIndex;
                if (isWideType(paramTypes[i])) {
                    nextIndex += 2;
                } else {
                    nextIndex++;
                }
            }
            return lvtIndex;
        }

        private static boolean isWideType(Type aType) {
            // float is not a wide type
            return (aType == Type.LONG_TYPE || aType == Type.DOUBLE_TYPE);
        }

        @Override
        public void visitLocalVariable(String name, String description, String signature, Label start, Label end,
                                       int index) {
            this.hasLvtInfo = true;
            for (int i = 0; i < lvtSlotIndex.length; i++) {
                if (lvtSlotIndex[i] == index) {
                    this.parameterNames[i] = name;
                }
            }
        }

        @Override
        public void visitEnd() {
            if (this.hasLvtInfo || (this.isStatic && this.parameterNames.length == 0)) {
                // visitLocalVariable will never be called for static no args methods
                // which doesn't use any local variables.
                // This means that hasLvtInfo could be false for that kind of methods
                // even if the class has local variable info.
                memberMap.put(resolveMember(), parameterNames);
            }
        }

        private Member resolveMember() {
            ClassLoader loader = clazz.getClassLoader();
            Class<?>[] classes = new Class<?>[args.length];

            // resolve args
            for (int i = 0; i < args.length; i++) {
                classes[i] = ClassUtils.resolveClassName(args[i].getClassName(), loader);
            }
            try {
                if (CONSTRUCTOR.equals(name)) {
                    return clazz.getDeclaredConstructor(classes);
                }

                return clazz.getDeclaredMethod(name, classes);
            } catch (NoSuchMethodException ex) {
                throw new IllegalStateException("Method [" + name
                        + "] was discovered in the .class file but cannot be resolved in the class object", ex);
            }
        }
    }

}
